1. Field of the Invention
This invention relates generally to a uniform speed lens drive arrangement for an auto focus camera and, more particularly, to a lens drive arrangement for an auto focus camera which operates at a uniform speed regardless of variations in the camera power supply.
2. Description of the Prior Art
Photographic camera apparatus embodying both shutter blade mechanisms of the scanning type as well as rotatable lens mechanisms which may be automatically focused in accordance with determined camera-to-subject range are well known in the art as described in U.S. Pat. No. 4,167,316, entitled "Sonar Controlled Lens Focus Apparatus", by Bruce K. Johnson et al., issued Sept. 11, 1979, in common assignment herewith and U.S. Pat. No. 4,192,587, entitled "Proportional Fill Flash", by Arthur G. LaRocque et al., issued Mar. 11, 1980, in common assignment herewith and both of which are now incorporated by reference herein. Scanning shutter blade mechanisms of the aforementioned type generally embody two shutter blade elements disposed in overlapping relationship for counter-reciprocating motion with respect to each other. The shutter blades are interconnected by a blade connecting member generally called a walking beam. The blade connecting member is rotatably mounted to drive the shutter blade elements to define a progressively increasing aperture size. As is shown in U.S. Pat. No. 4,167,316, supra, it is convenient to utilize the initial movement of the blade connecting member to also set the lens mechanism into rotation.
Since the rotating lens mechanism must be stopped at the appropriate focal position corresponding to a previously determined camera-to-subject distance, it is necessary that the rotational dynamics of the lens mechanism be as predictable as possible particularly for systems where the lens stopping command is provided without benefit of a positive feedback signal to positively identify the instantaneous focal position of the lens mechanism. Thus, although it may be convenient to utilize the blade connecting member to set the rotatable lens mechanism into rotation, it may not always be possible to drive the lens mechanism at a uniform rate since variations in the camera battery supply output may affect the speed at which the blade connecting member is driven. Thus, if the speed of the blade connecting member varies in concert with variations in the output of the camera battery supply, there will be imparted a corresponding variation to the rotational speed at which the lens mechanism is driven thereby making the rotational dynamics of the lens mechanism unpredictable. With such unpredictable rotational dynamics, it becomes difficult if not impossible to stop the lens mechanism at the appropriate focal position particularly for an open loop system where there is no feedback signal provided relative to the exact focal position of the lens mechanism.
Therefore, it is a primary object of this invention to provide a lens drive system for an auto focus camera wherein the lens is driven at a uniform rate regardless of variations in the output of the camera battery supply.
It is a further object of this invention to provide a lens drive mechanism wherein the lens mechanism is driven at a uniform rate by way of a shutter blade connecting member regardless of variations in the output of the camera battery supply which affect the rotational speed at which the shutter blade connecting member is driven.
Other objects of the invention will be in part obvious and will in part appear hereinafter. The invention accordingly comprises a mechanism and system possessing the construction, combination of elements and arrangement of parts which are exemplified in the following detailed disclosure.